Buck Converter Soft Start for Inrush and Overshoot Control
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Solution Overview
Problem
Buck converters face performance issues such as inrush current at startup and overshoot of output voltage, necessitating a soft start function to improve their startup behavior.
Innovation Solution
A switched-mode power supply (SMPS) with a Buck converter and a control circuit that includes a comparator, pulse-width modulator, AND gate, pulse generator, and selection circuit. The control circuit generates timing-varying pulse-width modulated signals based on a reference voltage that increases from a first to a second voltage, allowing the Buck converter to be controlled effectively during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Buck converter is started up directly without soft start control, then the startup process is simple and fast, but inrush current occurs and output voltage overshoots
Solution Approach 1:
The control circuit performs preliminary action by generating a soft start control signal before normal operation begins. This signal gradually increases the duty cycle from zero to its target value, preparing the converter for stable operation and preventing inrush current and voltage overshoot at startup.
Solution Approach 2:
The control circuit dynamically adjusts the duty cycle based on the startup stage. During soft start, the duty cycle increases gradually; once the output voltage reaches the reference level, the control switches to normal PWM mode. This dynamic adaptation resolves the contradiction between simple startup and stable operation.
2Reliability
If a soft start function is implemented to reduce inrush current and voltage overshoot, then startup stability improves, but the control circuit complexity increases
Solution Approach 1:
The soft start function is merged with the existing PWM control circuitry. The control circuit integrates the soft start signal generation and PWM modulation in a unified structure, sharing common components such as the comparator and control logic, thereby reducing overall circuit complexity while maintaining soft start functionality.
Solution Approach 2:
The control circuit is designed with multi-functionality, serving both soft start and normal PWM control operations. The same control circuit generates different control signals based on the operational stage, eliminating the need for separate dedicated soft start hardware and reducing component count.
Data Source
AI summary
An integrated circuit device includes: a Buck converter; and a control circuit for the Buck converter, which includes: a comparator configured to compare a feedback voltage of the Buck converter with a reference voltage that increases from a first voltage to a second voltage; a pulse-width modulator configured to generate a pulse-width modulated (PWM) signal having a timing-varying pulse width proportional to the reference voltage; an AND gate configured to generate a first control signal by performing a logic AND operation on an output of the comparator and the PWM signal; a pulse generator configured to generate a second control signal by generating a pulse in response to a rising edge in the output of the comparator; and a selection circuit configured to, based on an output voltage of the Buck converter, select the first control signal or the second control signal as a control signal for the Buck converter.